The invention relates to an operating mechanism for a high-voltage circuit-breaker having a coupling device of the freewheel type between an electric motor and the trigger shaft of the operating mechanism, said coupling device comprising first and second friction members coaxially mounted along a secondary shaft, said secondary shaft being rotatably mounted to rotate in a predetermined direction when a spring-loaded mechanism that acts on the device relaxes, it being possible for the second friction member to freewheel about said secondary shaft in said predetermined direction at a speed of rotation that is lower than the speed of rotation of the secondary shaft, it also being possible for said second friction member to be rotated by the motor in said predetermined direction, and to become constrained to rotate with the first friction member so as to recock said spring-loaded mechanism.
In such an operating mechanism, the trigger shaft is moved by the spring which is a closure spring, and it moves the shaft which is a main shaft via a cam. In this way, the circuit-breaker is closed at the same time as an opening spring is tensioned.
In operation, the spring-loaded system is recocked after the spring has relaxed, by the motor rotating, the trigger shaft turning in the same predetermined direction of rotation when it is driven by the motor and when it is driven by the spring-loaded mechanism. The freewheel-type coupling device is designed such that the spring-loaded mechanism relaxing and thereby rotating the trigger shaft does not rotate the motor, which would slow down the speed of the trigger shaft, and thereby reduce the effectiveness of the operating mechanism.
In known operating mechanisms, the coupling device is generally implemented with a conventional freewheel, such as, for example, in U.S. Pat. No. 4,762,971. In that patent, the two friction members are formed by two coaxial rings between which balls are disposed. More particularly, the first friction member is a small-diameter ring which is mounted in fixed manner on the shaft, and the second friction member is a larger-diameter ring surrounding the first ring, as in the general configuration of a conventional ball bearing. Each ball is oval in shape and is held in a certain angular position by a spring so as to be continuously in abutment against both friction members. Depending on the direction of relative rotation of the friction members formed by the rings, the balls tend to be braced between the two rings to couple the device, or else to allow the rings to slide to decouple the device.
With that construction, regular maintenance of the operating mechanism is necessary for it to operate properly. Proper operation of such a device depends to a large extent on greasing: under-greasing can lead to wear and to the device binding, which slows down the circuit-breaker closure operation, while over-greasing reduces the torque that can be transmitted through the device, which prevents the motor from tensioning the closure spring fully. In addition, the high pressure to which the balls and their tracks are subjected makes it essential to use components that are of high quality and that are precision manufactured, which leads to a manufacturing cost that is high. Those elements are very sensitive to overloading, even overloading for a short time.